Various methods have been proposed for fitting a rotor core and a rotating shaft with each other in a rotor of a rotating electric machine, including the one as proposed in Japanese Patent Laying-Open No. 61-102140.
A rotor for example disclosed in Japanese Patent Laying-Open No. 2004-32943 includes a key member provided on the inner wall of the rotor to extend toward the center of the rotor, and a key groove formed in the outer wall of the shaft. The key groove and the key member are formed in such a manner that circumferential rotation of one of the key groove and the key member relative to the other is allowed in the process where the key groove and key member are fitted with each other.
In this rotor, the stress generated between the rotor core and the rotating shaft while the rotor core and the rotating shaft are fitted with each other is reduced.
A rotor disclosed in Japanese Patent Laying-Open No. 2006-217770 includes a rotor core formed by stacking a plurality of thin steel sheets having respective through holes formed therein, and a shaft that is press-fit in a fit-in hole formed in the center of the rotor core. The rotor core is formed by making respective through holes in the thin steel sheets, and stacking the thin steel sheets in such a manner that smaller diameter portions and larger diameter portions of the through holes are alternately arranged in the axial direction. Further, the shaft having a roughened portion where protrusions and depressions are formed on its outer peripheral surface is press-fit in the fit-in hole of the rotor core. In this way, the rotor for a motor is structured.
The above-described conventional rotor disclosed in Japanese Patent Laying-Open No. 2004-32943, however, has a problem of iron loss due to stress concentration on the key member while the rotor core and the shaft rotate together.
Other publications, Japanese Patent Laying-Open Nos. 2006-217770 and 61-102140 do not disclose or suggest the problem of iron loss caused by stress concentration on the key member while the rotor core and the shaft are rotating together.
Here, in order to restrain stress concentration on the key member, the following method may be used. For example, in the surface of the rotor core, a groove depressed away from the surface of the rotating shaft is formed adjacent to the key member. In this way, a large stress is restrained from being generated between the key member and the key groove.
Even if such a groove is formed, however, a moment could be concentrated on a part of the inner surface of the rotor core that defines the groove, depending on the shape of the groove. Here, the problem of iron loss still arises.